The subject invention generally relates to a robot calibration system for calibrating a robot and a method of determining a position of the robot relative to a calibration object that is external to the robot. More specifically, the subject invention relates to the robot calibration system having an electrically-charged calibration object that enables the position of the robot to be determined when the robot electrically interacts with the electrically-charged calibration object.
Robots are utilized across many industries to conduct various operations on workpieces. A robot includes a robot arm having a tool surface, or tool, for conducting the various operations on workpieces. As one example, a robot may include a waterjet tool that is utilized to cut through a particular workpiece. Generally, it is required that the robot is calibrated in order to accurately conduct an operation on a workpiece. It is also required that the robot maintain calibration throughout the operation to ensure that the robot is able to repeat the operation. However, as robots conduct the various operations, the calibration of the robot frequently changes due to uncontrollable and/or inadvertent events, such as an inadvertent collision with the workpiece. As such, it is necessary to have systems and methods for calibrating the robot. As appreciated, systems and methods for calibrating the robot are critical to the safe and optimal utilization of robots in industries such as arc welding, spot welding, waterjet cutting, and dispensing.
Systems for calibrating robots are known in the art. Similarly, methods of determining a position of a robot for purposes of calibrating the robot are also known in the art. The conventional systems and methods for calibrating robots utilize electrical continuity to detect contact between the robot and a calibration object. Once the contact between the robot and the calibration object is detected, the position of the robot relative to the calibration object can be determined, and the robot can be calibrated.
The conventional systems and methods that rely on electrical continuity electrically charge the tool disposed on the robot and electrically ground the calibration object in order to detect contact between the robot and calibration object. The systems and methods of the prior art that electrically charge the tool disposed on the robot are inadequate because they are unduly burdensome as electrically-charged robot tooling is not easily achieved. More specifically, to electrically charge the tool, these systems and methods ignore the fact that the robot is typically already grounded and, instead, require additional electric circuitry and other components to override the ground of the robot and to charge the tooling. Furthermore, these systems and methods may be considered unsafe. For example, if the tool disposed on the robot is a spot weld tool, then great care must be observed to ensure that high process voltages and currents associated with the spot weld tool are not inadvertently applied during calibration. Also, when using electrically-charged tooling, a robot operator may be required to approach the robot to connect additional electric circuitry required for a complete circuit. An example of such a conventional system and method is disclosed in U.S. Pat. No. 5,910,719 to Thorne. Specifically, the ""719 patent to Thorne requires that an alligator clip, i.e., additional electrical circuitry, be connected from a spot weld tool to the calibration object, and more likely than not, the robot operator would be responsible for approaching the robot and making this connection. A further example of such a conventional system and method is disclosed in U.S. Pat. No. 4,558,312 to Yonemoto et al. The ""312 patent to Yonemoto et al. charges the tool and grounds the calibration object.
In sum, the conventional systems and methods for calibrating robots that rely on electrical continuity, as detailed above, are characterized by one or more inadequacy. Due to the inadequacies identified in the prior art, it is desirable to provide a novel robot calibration system and method of determining a position of a robot relative to an electrically-charged calibration object for calibrating the robot that is safe and is not unduly burdensome.
A robot calibration system is disclosed. The robot calibration system according to the subject invention is utilized for calibrating a robot. A method of determining a position of the robot relative to a calibration object is also disclosed. The position of the robot relative to the calibration object is also utilized for calibrating the robot. The robot calibration system includes a ground. The ground defines a return for an electrical circuit. The robot is electrically connected to the ground and includes at least one robot arm having a tool surface operating within a robot workspace.
The robot calibration system also includes an electrical supply and a detection device. The electrical supply defines a source for the electrical circuit. The source provides an electrical charge and a calibration reference voltage to the calibration system. The detection device of the robot calibration system is in electrical communication with the electrical supply. The detection device detects a variation in at least one of the electrical charge and the calibration reference voltage. That is, the detection device detects the variation in the electrical charge, in the calibration reference voltage, or in both the charge and the voltage.
The robot calibration system further includes a calibration object external to the robot. The calibration object is electrically insulated from the ground and is electrically connected to the electrical supply. The calibration object receives the electrical charge and the calibration reference voltage from the electrical supply. In operation, the robot is moved from an initial position, where the tool surface is spaced from the calibration object, toward the calibration object such that the tool surface electrically interacts with the calibration object. When the tool surface of the robot electrically interacts with the calibration object, the detection device detects a variation in at least one of the electrical charge and the calibration reference voltage. As such, the position of the robot relative to the calibration object can be determined upon the electrical interaction between the tool surface of the robot and the calibration object for calibrating the robot.
Accordingly, by utilizing an electrically-charged calibration object and not charging the tool surface of the robot, the subject invention provides the unexpected advantage of minimizing the amount of electrical components required to detect variations in the electrical charge and in the calibration reference voltage provided to the calibration object. The subject invention also enhances operator safety as it does not require an operator to approach the robot thereby minimizing any risk of injury to the operator. Also, by electrically-charging the calibration object, and not the tool on the robot, the subject invention takes advantage of the existing ground for the robot. Furthermore, the subject invention optimizes the calibration of the robot by providing for automatic and unattended calibration of the robot without changes or additions to existing robot tooling.